Present automatic air carbon-arc torches are large and heavy in comparison to automatic welding devices thus requiring mounting to heavy duty travel systems and positioning devices. Moreover conventional devices have the majority of their exposed surfaces electrically conductive, require adjustment and/or part replacement when changing electrode diameters. The prior art devices encourage electrode breakage subsequent internal electrode jamming and electrode shorting to the case. Furthermore, electrical arcing of contact shoes is common and results in ruined work and premature failure of the torch parts.
One type of automatic Air Carbon-Arc Cutting and Gouging Torch is disclosed in U.S. Pat. No. 3,317,779. In this patent, rollers are used to frictionally engage the electrode and feed it through a nozzle containing a contact shoe which conducts electricity to the electrode. The nozzle has provision for directing air along the electrode to the arc and includes means for pivoting the housing support drive rolls having a fixed position relative to each other about an axis to, in effect, change the spacing between the rollers and increase frictional contact with the electrode.
Means for controlling the torch including the spacing of the torch to the workpiece and feeding of the electrode are disclosed in U.S. Pat. No. 3,659,071. This patent is an improved version of an automatic torch and control system.
Jointed electrodes afor use in automatic torches are disclosed in U.S. Pat. No. 3,131,290.
Lastly, the current state of the art is reflected in the Model N automatic Air Carbon-Arc Cutting and Gouging Torch manufactured and sold by the Arcair Company of Lancaster, Ohio, and as shown in U.S. Pat. No. 4,260,867.
U.S. Pat. No. 4,300,033 discloses a device wherein the well known Coanda effect is used to entrain ambient air into the process air of a manual air carbon-arc cutting and gouging torch. The device of the '033 patent shows an annular flow of air completely surrounding the electrode which although creating less noise is wasteful of process air and does not remove slag well nor produce a quality groove.
Among the problems with the prior art torches is the problem of "stub-out" which, in turn, causes breakage of the electrodes. In most prior art devices internally of the automatic torch, the electrode is fixed between drive and idler rollers which are spaced apart from a pair of contact shoes which also serve to constrain movement of the electrode. If, when the torch is being used, the electrode is driven too close to the workpiece, it can actually contact the workpiece and cause a condition which is known as "stub-out". When this happens in prior art devices, a bending stress is placed on the electrode since it is fixed at two or more points inside the torch. This transverse load can cause breakage of the electrode where the electrode is constrained at the drive mechanism and at the shoe assembly, thus jamming the electrode inside the torch requiring the torch to be disassembled to extricate the broken electrode.
In prior art devices when the bending moment is applied to the electrode, arcing can occur between the electrode and the contact shoe causing a localized hardening of the contact shoe, the localized hardened spots on the contact shoe causing excessive wear of the electrodes subsequently used with the torch.
Furthermore, the prior art devices generally contain a very complex structure for effecting both the driving of the electrode and the carrying of current to the electrode via the contact shoes which support the electrode at a location spaced from the drive rolls.